With development of technologies, in a technology such as a sparse code multiple access (SCMA) technology or an orthogonal frequency division multiplexing (OFDM) technology, multiple terminal devices have been allowed to multiplex a same time-frequency resource to transmit data, that is, a transmit end device may perform encoding and modulation on multiple layers of information bits that need to be transmitted in order to generate multiple layers of modulation symbols, and after performing superposition processing on the multiple layers of modulation symbols on the time-frequency resource, send the superposed modulation symbols to a receive end device using an air interface.
Currently, a multiple-input multiple-output (MIMO) technology is known, that is, a transmit end device and a receive end device may perform data transmission using multiple antenna ports, to improve a system capacity and transmission reliability.
Therefore, it is expected to combine the MIMO technology with a multiplexing technology such as SCMA or OFDM in order to further improve performance of a communications system.
How to combine the foregoing MIMO technology with the SCMA technology or the like in order to further improve the system capacity and transmission reliability is an urgent problem to be resolved.
A feasible solution is that after superposition processing is performed on multiple layers of modulation symbols on a time-frequency resource, a transmit end device may perform precoding processing on a generated signal that is carried on the time-frequency resource in order to generate transmit signals corresponding to antenna ports.
However, in this solution, a space diversity gain cannot be effectively used. For example, when signals of multiple terminal devices are carried on a same time-frequency resource, after the foregoing precoding processing is performed, signal components of multiple users are sent using a same port, respective optimal antenna ports of the signal components cannot be selected simultaneously, and mutual interference between components causes a relatively high bit error rate during decoding by a receive end, severely affecting communication reliability.